Are the originals fried and you need to replace them or are you just trying to upgrade the amp?

When repairing my 250, I ordered the original 88/91 outputs, but the power supply uses IRF3205.

Another user on this forum, Clipped, uses BD909/910 as outputs with 3205's in the power supply of his rebuilt 2150SX (same board as 250). I think he has also used BD911/912 as outputs. He also uses 909/910 as replacements for the hard to find MPSU07/57 drivers, but you have to bend the leads to match the 07/57 pinout.

I'm just doing an upgrade for the hell of it. I wanted to experiment with it.
As of right now the amp works but the outputs are not matched anymore, so I figured I'd upgrade it and match the outputs at the same time. I saw the posting on the bd911 and 912 i was just wondering what all my options where. Would I need to upgrade the power supply to support the better outputs?

The BD parts are 90 watt devices. The 911/912 devices are 100V and the 909/910 are rated to 80V. The original 2n6488/91 devices are rated at 80V, 75W.

The 909/910 are a better match to the original parts, but have a higher power rating, 90W vs 75W.

I usually shop at mouser.com, but they don't carry the 909/910 devices, only the 911/912 combo.

IRF 3205's in the power supply with BD devices on the output side should work just fine.

When repairing my HCCA amps, I also replaced all capacitors in the power supply. You can install the same size caps with higher capacity. Be sure to install 105 degree parts as these amps get really hot.

Clipped went as far as changing the input opamp in his amps with good results.

Once you make all those changes, if you have access to a scope, you should check for oscillation on the output. Installing newer, faster, parts can cause the amp to oscillate at high frequencies.

Ok I went to check the amp out today before I go modifying things. The mono button doesn't seem to be working. The amp works fine until I push the mono button on, then it cuts out. What do you thinks going on?